Catalytic converters may be present in the exhaust stream of motor vehicles in order to reduce the emission of pollutants produced during combustion. For example, unburnt fuel, NOx, and CO may all be converted to less toxic substrates before being released to the atmosphere.
However, as a catalyst ages, its performance may deteriorate, leading to increased emissions. To determine the age of a catalyst, the temperature of the substrate wall may first be estimated. The temperature of the substrate wall of a catalytic converter can be estimated using the measured temperature of the gas in a position upstream, the estimation of the level of unburned fuel in the exhaust gas upstream, the mass of the stored unburned fuel, the mass of stored particle material, and the thermal properties of the exhaust-gas aftertreatment element. If the temperature downstream is measured, an adaptation signal may be generated which is then used to more accurately estimate the temperature of the substrate wall.
Frequently, the adaptation signal is used directly with the energy balance of the catalyst in order to feed back the error in the estimation. Furthermore, the monitoring of the estimated increase in the exothermic temperature is compared with the situation of a damaged or aged catalytic converter and is used to prevent a state of aging being reached in which the pollutants reach a level above the defined limit value.
The inventors herein have recognized a number of issues with the above approach. First, no corrective actions regarding catalyst function are taken based on the adaptation signal. Rather, the adaptation signal is simply used to improve the estimation, and, if indicated, signal for catalyst replacement. Further, the adaptation signal does not take into account the gradual aging of the catalyst, and thus does not allow for adjustments to catalyst function over the course of the catalyst lifespan.
A method for a vehicle catalyst is provided. The method comprises if a difference between an estimated temperature and a measured temperature downstream of the catalyst is greater than a threshold, calculating an adaptation value. The method further comprises adapting the thermal model, adjusting an amount of reductant in an exhaust stream upstream of the catalyst, and indicating an aging state of the catalyst, based on the adaptation value.
In this way, the level of non-combusted fuel, or reductant, in the exhaust stream may be adjusted based on the adaptation value, and, in one example, the thermal model may be adapted by directly correcting for the energy balance of the catalyst. Finally, gradual adaptation of the thermal aging of the catalyst may be determined and accounted for, and then may be used to detect deterioration and/or absence of the catalyst.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.